It is known to use elongate structural members that are cold rolled from sheet metal to form typically open C-channel sections having a web with flanges projecting from the web edges. These C-channels normally have protective zinc based coatings and are substantially light weight due to the use of light gauge material. Such structural members are usually used in domestic housing, industrial and commercial buildings. When they are used as domestic housing wall frames, the series of regularly spaced parallel vertical structural members in the framework are commonly known as studs while the horizontal or complimentary encasing members are commonly known as plates. The plates can be used to form heads and sills for door openings and window openings respectively.
Frameworks made from these known C-channel members are generally formed by nesting an open C-channel member in a mating C-channel member. This is achieved by having the internal dimensions of the plate matching the external dimensions of the mating studs, and in this way, all the C-channel members have square cut ends. As an example, stud members nest in plate members and noggin members nest in stud members.
Connections made between members of these types are generally made by welds, clinches, bolts, screw, rivets and the like. The use of nails which is the preferred connections between timber structural members is unacceptable for connections between these structural steel members. The use of nails is considered the most efficient means of connection between structural members, however, in nailing timber stud members to timber plate members, the connection is made by driving the nails through the rear of the plate members into the end of the stud members parallel to the longitudinal axes of the stud members. This results in the strength of the joint in the direction of the longitudinal axis of the stud to be dependent on the clamping action of the timber fibres on the shank of the nail. This connection requires reinforcement by metal strapping when the loading on the connection is applied in instances such that the connection is a bracing point and when uplift loading is experienced from wind uplift pressures on sheeted roofs and the like. It has been found that connections incorporating nails in this way are relatively inefficient because the inherent strength of the steel nail is not used whereby the strength of the clamping action on the shank of the nail is less than the tensile strength of the nail. Similarly, the shear capacity of the nail is not being maximised in this type of connection.
It is believed that the most efficient means of utilising the connecting capacity of a nail is by designing a joint which applies shear loading to the nail. In timber framework assemblies pure shear can be achieved by using metal straps and nailing. Semi-shear can be achieved by skew nailing. Both these methods cannot achieve the allowable shear of the nail because of the lack of strength of the timber. In the known framework assemblies which utilise steel C-channel members as previously described, this form of connection is not viable. The nail passes through the flange of the C-channel member plate into the flange of the mating C-channel member stud and likewise a nail can be installed in the opposite side. The nail twists and disengages from the mating flanges under loading that pulls the stud away from the plate in a direction parallel to the longitudinal axis of the stud. Therefore it is desirable to have steel structural members which have inherent design features that allow effective connections to be made by using the shear capacity of the fasteners, preferably nails, whereby there are at least two distinct points of shear loading along a single nail.
When such framework, as previously described, is used in walling applications which have cladding, it is known that wind loading on the cladding causes horizontal reaction forces to occur between the flange of the end of the stud member and the flange of the plate member immediately adjacent the bend radius of the plate members furthest from the windward face of the framework. This concentration of forces can cause the opposing flange of the plate member to "open up", bearing failure of the contacting stud end corners and adding extra loading on the stud to plate connections. Therefore it is desirable to provide steel structural members and connections therebetween which distributes these reaction forces so as to not cause failure of the framework.
In the design of roll formed steel members minimum bend radii are required to minimise cracking of the bend during the roll forming process. Such minimum bend radii reduces the strength of joints under load application where the joints comprise stud and plate members in which the stud members nest against the tops of the bend radii of the plate members. This applied compression loading causes the flanges of the plate members to deform outwardly as the bends in the plate members deform under the forces from the flanges of the stud members. A known method of plate design which provides uniform support to the cross-section of the stud member is to form the radii into the base of the flanges of the plate members with the radii causing bulges outwardly of the plane of the flanges. This plate design causes installed cladding such as wall linings, preferably plasterboard, to stand proud of the plane of the wall face where the wall lining extends past the web of the plate members and when the plate members are notched and used as head and sill members in door and window openings respectively. Therefore it is desirable to overcome this problem by protruding the bend radii of the plate members, which results in the bulges extending from the plane of the webs and not the plane of the flanges.
When the framework is used as wall frames in tiled roof domestic housing buildings, the preferred means of joining the framework, as previously described, to concrete slabs and the like to provide holddown to resist overturning and bracing loads, is by nailing masonry nails through the bottom plate members into the concrete slab. When using the C-channel steel frame members the hammer driven masonry nails require additional installation support which is usually provided by driving the masonry nails through a timber block which fits into the C-channel. Without the timber block it is difficult to hammer the nails due to the high impact force required to penetrate the plate web when it is in direct contact with the concrete slab because the normal nail piercing action is hindered and because of the associated safety issues with nail mishits.
In sheeted roof domestic construction other fasteners such as chemsets.RTM., dynabolts.RTM., cast in bolts and other forms of pre-drilled fasteners are used to provide holdown to concrete slabs. Large washers are used to transfer the restraining forces of these fasteners to the adjacent flanges when the fasteners are installed adjacent to the stud to plate connection joints. Thus it is seen that it is desirable to provide a means by which a masonry nail or other fastening means can be easily installed without additional nail support such as a timber block and to reduce the requirements for washers in the connections as described in the above installations.
It is widely accepted in domestic construction trade work that nailing is the most cost efficient means of fixing architraves and skirting and is accomplished usually by means of pneumatic or gas powered nailing guns. The only known method to achieve this method of fixing the architraves and skirting is to use a timber infill to the window and door openings and timber blocks to the bottom wall plate members in order that the nails are fully supported, other than using costly alternatives such as screwing and the like. Thus it is deskable to have a framework which does not require timber infills or blocks while maintaining the cost effectiveness of the preferred gun nailing method for fit out of the construction.
In timber framework construction it is common practice to skew nail connections, for example, ceiling joist to top plate, jack, creeper and hip rafter to top plate. In similar constructed frames using conventional C-channel members skew nailing through the webs of the of the C-channel members cannot be achieved because it is impossible to drive a nail through at an angle to the flat web. The same also applies to the flat flanges of the C-channel members. This inability to be nailed at an angle is usually overcome by installing an angle bracket which provides a fixing point and support for the nail via the base of the bracket and a screwed connection through the vertical bracket leg into the web of the C-channel members. It is therefore desirable to have a structural member which allows for skew nailing.
Where joints are formed between stud members and sill members and stud members and window and door head members, the head or sill members are normally plain unlipped C-channel notched at both ends. The ends of the web of C-channels are notched to allow the remaining tags of the flanges to encase the stud member so that there is a flange to flange connection at both sides of the stud members. Joints formed in this way have diminished lateral rigidity against loading applied in the plane of the web of the sill/head members perpendicular to the longitudinal axis of the sill/head members. This is because the elements that form the remaining tags have small flexural rigidity in the plane of loading and the lateral deflection will increase due to assembly clearances which frequently occur between the notched webs of the sill/head members and the webs of the adjacent stud members.
Such lateral loading on the sill/head members cause tensile stresses in the remaining tags on the same side of the applied loading causing shear loading on the flange to flange connection. To overcome this problem angle brackets are used provide the connection between the webs of the sill/head members and the webs of the stud members. This proves to be uneconomical due to the double fastening which is used. Therefore it is desirable to have connections or joints which are formed from partial notching of the web elements of the plate members to form rigid head or sill connections, and stud structural members to form rigid stud to plate connections enabling interlocking of the web elements in addition to encasing the mating structural members by the flange elements.
It is also desirable to provide the plate members with partial web notchings so that the protrusions of the web sections can nest and interlock with the corresponding web intrusions of the stud members.
In the construction of domestic buildings and the like a major labour and material cost is incurred in the assembly of the wall frames. This assembly usually takes the form of a manufacturing process which involves jigging of the wall frame to hold dimensional and shape characteristics while the fastening of the joints or connections occur which is generally semi-automatic.
In the assembly of timber frames the manufacturing process involves the use of a series of pneumatically operated nail guns to join the plate members to the stud members, usually one stud at a time. This process usually involves firing 2 of 75 mm long 3.08 mm diameter nails or similar into the joint formed at each end of the stud members whereby each stud requires four nails.
In the assembly of steel structural members into wall frames many different methods of manufacture are known. These methods include welding, screwing, riveting, clinching and using a built in fastening system such as corresponding tabs and slots. The effectiveness of the tab and slot form of assembly decreases as the thickness or gauge of the structural member decreases and the material costs associated with the tab and slot form is great due to the manufacturing process of forming the tabs. Welding is not suitable for steel gauges less than 0.75 bmt and there are further costs associated with repair of damaged surfaces. This has resulted in the non viability of welding as the form of connection. Clinching and other forms of connections have high costs associated with their semi-automation so these methods are usually applied manually which thereby increases the labour content of the costs of manufacture.
Therefore it is seen that it is desirable to have a means by which the manufacturing of steel wall frame can be assembled more economically than known methods.